Most personal computers (PCs) and laptops include audio speakers to play music and soundtracks for videos, and to play audio files for applications and games. As shown in FIG. 4A (prior art), traditional audio processing for PC applications and games are designed for a single listener 96 positioned in front of the PC with speakers 94a and 94b disposed on opposite sides of a display monitor 92. A subwoofer speaker (not shown) may also be included to provide enhanced bass response of an acoustic field 98 centered on the listener. Some systems include surround sound speakers, such as two speakers 94c and 94d that are disposed behind and to the sides of the listener, as shown in FIG. 4B. These surround sound speakers provide enhanced enjoyment by producing a rear surround acoustic field 99.
With at least two speakers, the sound can be panned between the left and right side of the display, giving the listener the impression that sounds are coming from the right or left, or if equal, from the center of the display. With four speakers, the sound can also be panned between the right and left behind the listener and/or between either pair of the front and rear speakers. Four or more speakers can also be used for special audio effects, such as an echo effect that is produced by driving the rear speakers with a slight time delay to give the user the impression of a reverberant sound field in a large chamber, even though the speakers are located in a small room. Head-related transfer function (HRTF) algorithms can also be used to create the impression of sound behind the listener, even when only two speakers 94a and 94b are provided, as in FIG. 4A. There are a number of techniques for positional audio with various layouts of speakers around a listener. One example is the DirectSound 3-D system used in Microsoft Corporation's Windows™ operating system. Such techniques assume that the listener will be at a certain sweet spot relative to the speakers. The sweet spot is generally at a position in front of the display and approximately at one vertex of an equilateral triangle, with the two front speakers disposed at the other two vertices of the triangle, producing sound field 98.
The conventional approach for positioning speakers assumes that the user will be viewing a generally vertical display and providing input with a conventional keyboard and/or pointing device. However, a new type of interactive display system has been developed that requires a different arrangement of speakers. In this new interactive display system, the display surface displays text and graphic images, just as on a conventional display, but the new interactive display system includes a display surface that is also responsive to objects contacting or proximate to the display surface. For example, a user can touch the display surface with an object or move an object, such as a finger, just over the display surface to provide an input to an application. While other approaches are contemplated, an initial exemplary embodiment employs an optical sensor for sensing objects in contact with or proximate to the display surface. The interactive display surface of the initial exemplary embodiment is rectangular in shape and horizontal. A vertical or angled interactive display could also be used, and the interactive display surface could be round, oval, or some other shape besides rectangular. Furthermore, this exemplary embodiment of the interactive display system is relatively large and the housing for the interactive display surface appears to be a table top. This embodiment was designed to support multiple users surrounding the table or a single user who may approach the table from any side.
Clearly, in determining where speakers should be provided, the interactive display system doesn't conform to the conventional paradigm of a user seated in front of a PC. Several questions arise in regard to implementing an audio system for an interactive display system that is horizontal and can be approached from any side:                Where should speakers be placed on the interactive display system?        Since the interactive display surface can be used from multiple sides, how should the audio be adjusted according to a user's position?        Multiple users may simultaneously be accessing separate applications or taking separate actions in a game or other application, resulting in a cluttered audio landscape. An audio cue played from all speakers on the table may indicate what happened in an application, but not indicate which user provided an input resulting in the cue. It would therefore be desirable to use speaker positioning to create a less cluttered audio landscape. How should this be done?        When representing a virtual object that emits sound on the display surface, it would be desirable to generate audio in such a way that it will sound like the audio comes from the object's position, and if the object moves, the corresponding sound location should appear to move with the virtual object. How can this feature be implemented?        
Accordingly, it would be desirable to develop a novel approach for disposition of speakers useful with a horizontal interactive display system to provide an effective acoustical experience for one or more users of the system. The speakers should be disposed to enable one or more users to experience the acoustical field appropriate to their disposition, regardless of the side of the interactive display surface where the use is located. Further, the sound produced by an application should drive the speakers in such a way as to relate to events in an application with which the sound is associated as well as the position(s) of one or more users around the display.